A climb-assisted model of charged dislocations under applied electromagnetic fields for predicting crack nucleation in battery materials
File(s)
Author(s)
Ning, Dongxue
Type
Thesis
Abstract
Many experimental observations show that dislocations play an important role in degrading the performance of lithium-ion batteries. An investigation of crack nucleation caused by the accumulation of the dislocations is carried out using discrete dislocation plasticity to seek potential methods of impeding this degradation. The new discrete dislocation plasticity model includes glide and climb, as well as the effect of the charged dislocations and the application of electromagnetic fields. Stroh’s method of predicting crack nucleation based on distributed stress is implemented in the simulation. The mechanism of charged dislocation transport in ionic crystals is proposed and the feasibility of applying discrete dislocation plasticity theory to LiFePO_4 is justified. Electroplasticity, magnetoplasticity and electromagnetic plasticity are studied in the ionic crystal. Taking into consideration the criteria of crack nucleation, the number of cracks nucleated in static electromagnetic fields in the ionic crystal is studied in terms of the dislocation structure, the grain size, the source and obstacle densities and the strain rate (neglected of volume change). Also, the number of cracks is studied in both static and cyclic electromagnetic fields in LiFePO_4 at both the partial strain (fast charging) and full strain.
The model is validated by reproducing the published findings for limiting cases and by successfully predicting the flow stress drop of NaCl when the electric field is applied, as compared to experimental observations. The results confirm that the climb promotes the effect of dislocation starvation regardless of the size of the sample. The applied electric field reduces the flow stress, and the combination of electric and magnetic fields reduces the flow stress even further. The electrical field is found to increase the number of cracks...
The model is validated by reproducing the published findings for limiting cases and by successfully predicting the flow stress drop of NaCl when the electric field is applied, as compared to experimental observations. The results confirm that the climb promotes the effect of dislocation starvation regardless of the size of the sample. The applied electric field reduces the flow stress, and the combination of electric and magnetic fields reduces the flow stress even further. The electrical field is found to increase the number of cracks...
Version
Open Access
Date Issued
2023-03-09
Date Awarded
01/07/2023
License URL
Advisor
Balint, Daniel
Publisher Department
Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)